The present application relates to an input level triggering device and a frequency dividing system, and particularly relates to an input level triggering device which can operate as a multiplexer and a frequency dividing system comprising the input level triggering device. FIG. 1 is a block diagram illustrating a conventional frequency dividing system. As shown in FIG. 1, the input level triggering devices D_1, D_2, D_3, D_4 are coupled in series. At least two input level triggering devices can form a frequency dividing device, the frequency dividing ratios of the frequency dividing depend on the numbers of input level triggering devices. In this example, two input level triggering devices constitute a frequency dividing device. Therefore, frequency dividing signals FDS_1, and FDS_2 with different frequencies can be provided. The multiplexer M is applied to select one of the frequency dividing signals FDS_1, and FDS_2 to output.
The output terminal of the multiplexer M can serve as a frequency divider output signal FDO, and serves as an input signal INS transmitted back to the input level triggering devices D_1.
The frequency dividing signals can be generated by an even number of input level triggering devices, as shown in FIG. 1. The frequency dividing signals can be generated by an odd number of input level triggering devices as well.
However, such frequency dividing system may have large loading since a plurality of multiplexers are needed and a plurality of devices are coupled in series in such structure. One extra multiplexer also degrades phase noise performance and consumes more current.